The present invention relates to a device for coating webs of material traveling over a backing roll to a controlled thickness, in which the coating medium can be applied to the web with a slotted nozzle that extends over the total width of the web and in which the nozzle has an initial-flow regulation gap downstream of which a flow-regulation lip and an excess-removal lip demarcate a flow-regulation chamber.
A device of this type is known, from German Patent No. 2 359 413 for example. It has a fixed-adjustable flow-regulation gap that generates a coating excess in the vicinity of the flow-regulation lip. The flow-regulation gap requires very precise adjustment with respect to both the speed at which the web is traveling and to the rheology of the coating medium. Fine flow regulation is controlled up-web in the known device by means of a separate doctor mechanism.
It has been demonstrated that a circulating web of material can, especially when it is traveling at high speeds, force an isolating layer of air into the flow-regulation chamber, leaving certain points on the web uncoated. Furthermore, the coating weights that can be obtained are very light and the uptake of printing ink is not uniform enough for the quality now ordinarily demanded.